Quadrature networks are used in virtually all kinds of radio frequency circuits. In a quadrature network, two equal amplitude but phase-shifted output signals are generated from a single input signal. In an ideal quadrature system, the two output signals have a relative phase shift of π/2 radians (90°). Typically, quadrature networks produce an in-phase signal that leads the input signal by π/4 and a quadrature signal that lags the input signal by π/4, for a total π/2 phase difference between the two output signals.
Quadrature local oscillator (LO) signals are widely used in transmitter, receiver or transceiver systems. Low amplitude and phase errors are the basic requirements for quadrature LO signals. There are commonly three approaches for generating quadrature LO signals. A first is to use a passive or active phase shifter, or a 90-degree power divider, to split an LO signal into I (In-Phase) and Q (Quadrant) LO signals. Both the phase shifter and divider circuits are frequency dependant, meaning that they can only have the exact phase and amplitude balances at one frequency point or approximately a narrow group of frequencies by nature. Thus, the phase shifter and divider circuit approach is not robust because it is only usable for a very narrow range of frequencies. Moreover, it is generally difficult to fine tune the balances in such a system.
A second approach is to use coupled Voltage Controlled Oscillators (VCOs), in which the quadrature phase balance depends on the amplitude balance. However, this approach is disadvantageous because the phase balance suffers when the amplitudes are out of a balance due to any mismatches between the two coupled VCOs. Also, there is no mechanism for providing balance improvement in real time such that this approach does not provide a closed-loop scheme.
A third approach is to use master and slave latches to generate I and Q signals. However, this approach is difficult to implement at millimeter wave frequencies. Furthermore, this approach is disadvantageous in that it is not a closed-loop scheme.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.